When the oscillator which supplies the alternating drive voltage for a liquid crystal display fails, the circuit of the present application senses this condition and in response thereto removes the operating voltage from the liquid crystal driver transistors.

Both velocity and x-y deflection magnitude of a cathode ray tube (CRT) electron beam are continuously sensed, and beam intensity is limited to prevent damage to the CRT during periods of insufficient beam deflection.

A voltage at a control grid of a cathode ray tube is generated at a blanking level to provide beam current blanking when horizontal deflection loss occurs. The control grid voltage at the blanking level is developed in a capacitor prior to an instant in which the horizontal deflection loss occurs. When the capacitor voltage is applied to the control grid to provide the blanking level, the capacitor is discharged slowly. To maintain the capacitor charged, prior to such instant when horizontal deflection is lost, the capacitor voltage is not applied to the control grid as long as the horizontal deflection is normal, regardless of whether vertical deflection loss occurs. Either horizontal deflection loss or vertical deflection loss will disable a video driver stage that controls the cathode of the cathode ray tube for providing additional beam current blanking capability.